FIG. 1 is a representation of an apparatus that manufactures plastic film for products such as plastic shopping bags by a blown film extrusion process. A similar apparatus is disclosed in the U.S. Patent of Tewksbury et al., U.S. Pat. No. 9,044,896, which is assigned to the Assignee of this application and is incorporated herein by reference. In the process a hot plastic melt is blown as a tubular bubble 10 from an extrusion die 12. The tubular bubble 10 is blown upwardly through a bubble guide 14 to a collapsing frame 16. In the collapsing frame 16 the bubble 10 is folded flat. The flat folded bubble then passes over turning bars and continues on from the collapsing frame 16 for further processing.
FIG. 2 is an enlarged view of the collapsing frame 16. In the collapsing frame 16, the bubble 10 can be folded flat, or can be folded with gussets on the opposite sides of the bubble. The gussets are folded into the opposite sides of the bubble 10 by a pair of opposing gusset boards 18, 18′. The gusset boards 18, 18′ press the opposite sides of the bubble 10 inwardly as the bubble moves upwardly through the collapsing frame. This is represented in FIG. 3. In FIGS. 2 and 3 it can be seen that each of the gusset boards 18, 18′ are mirror images of each other. Therefore, only the one gusset board 18 to the right in FIGS. 2 and 3 will be described.
In FIGS. 2 and 3 it can be seen that the gusset board 18 has an elongate triangular sliding surface 20 that extends from a base edge 22 of the gusset board upwardly to an apex 24 of the gusset board. The sliding surface 20 faces toward the bubble 10 and engages the bubble 10 in sliding contact as the bubble moves upwardly through the collapsing frame 16. The gusset board 18 also has a pair of fold surfaces 26, 28 that extend upwardly along the opposite edges of the sliding surface 20. When the gusset board 18 is positioned in the collapsing frame 16 as represented in FIG. 3, as the bubble 10 moves upwardly the gusset board sliding surface 20 presses in on the side of the bubble and portions of the bubble are folded over the two fold surfaces 26, 28. This forms a gusset fold in the side of the bubble 10. In this manner, the pair of gusset boards 18, 18′ form gusset folds in the opposite sides of the bubble 10 as the bubble moves upwardly through the collapsing frame.
If gusset folds are not needed in the opposite sides of the bubble 10, then the gusset boards 18, 18′ are moved in the collapsing frame 16 to retracted positions away from the bubble 10. In FIG. 2, the gusset boards 18, 18′ are shown in their retracted positions relative to the collapsing frame 16. In these positions of the gusset boards 18, 18′ they guide the tubular bubble 10 upwardly and center the bubble 10 relative to the frame 16. In the positions of the gusset boards 18, 18′ shown in FIG. 2, the boards merely guide the tubular bubble 10 upwardly as the bubble is gradually flattened by the collapsing frame 16. The gusset boards 18, 18′ do not fold in the opposite sides of the tubular bubble 10.
Problems can be encountered in blown film extrusion apparatus such as that shown in FIG. 1 when the bubble 10 is desired to be folded flat without gussets. When the blown bubble 10 is not being folded with gussets, the gusset boards 18, 18′ have to be retracted or the board apexes 24, 24′ need to be moved away from each other to enable the full width of the bubble 10 to pass between the gusset boards 18, 18′ without being contacted by the boards. However, in almost all current blown film extrusion apparatus, there are obstructions that prevent the gusset boards 18, 18′ from moving away from each other. Obstacles like the supporting structures of the collapsing frame 16 prevent the gusset boards 18, 18′ from being separated completely from each other. In referring to FIG. 3, it can be seen that if the two gusset boards 18, 18′ were pivoted away from each other at pivot connections 32, 32′ the outward edges of the fold surfaces 26, 26′, 28, 28′ would engage against supporting structures of the collapsing frame 16. This would prevent the sliding surfaces 20, 20′ of the gusset boards 18, 18′ from being completely pivoted away from each other to where the sliding surfaces 20, 20′ are parallel and do not obstruct the movement of the bubble 10 upwardly through the collapsing frame 16. In current practice, blown film extrusion apparatus are either constructed to extrude the tubular bubble 10 that will be folded flat exclusively, or are constructed to fold gussets into the opposite sides of the tubular bubble 10.
Additionally, some film producers have purchased gusset boards 18, 18′ and have installed them on their blown film extrusion apparatus when they needed them, and removed the gusset boards 18, 18′ when they weren't needed. This is a laborious task that takes up to a day to remove the gusset boards, causing a significant drop in production capacity and efficiency throughout the course of a year. This has led to the development of the collapsible gusset board nose of this disclosure.